Low thermal expansion ceramic material, method of preparation and use

Abstract

This invention relates to the field of cordierite ceramic materials technology, and particularly to low thermal expansion ceramic materials, their preparation methods, and applications. The low thermal expansion ceramic material simultaneously possesses a low coefficient of thermal expansion, high density, and high flexural strength, exhibiting superior performance compared to traditional cordierite ceramics. It can meet the stringent requirements of semiconductor wafer manufacturing equipment and serve as a material for manufacturing wafer stages. Specifically, the coefficient of thermal expansion of the low thermal expansion ceramic material is 0.3–0.8 × 10⁻⁶. ‑6 / ℃, meeting the ultra-low expansion requirements of the wafer stage, and the density of the low thermal expansion ceramic material is ≥99.2%, which means that the surface of the low thermal expansion ceramic material is free of defects such as micropores and pits after precision polishing, and can meet the bearing requirements of ultra-high flatness of wafers; in addition, the low thermal expansion material has high mechanical strength, with a bending strength ≥200MPa and a compressive strength ≥1000MPa, so that the material will not affect the stability of equipment operation during the processing, assembly and long-term use of the low thermal expansion ceramic material.

Description

Technical Field

[0001] This invention relates to the field of cordierite ceramic materials technology, and in particular to a low thermal expansion ceramic material, its preparation method and application. Background Technology

[0002] In the semiconductor wafer manufacturing industry, the wafer stage, as a key component supporting core processes such as photolithography, etching, and thin film deposition, directly determines the precision and stability of wafer processing. To meet the precision requirements of wafer support and process compatibility, the materials used in the wafer stage must possess high density, ultra-high flatness, and chemical inertness. Furthermore, within the process temperature range of 20–150°C, the materials used in the wafer stage must maintain near-zero thermal expansion to prevent thermal deformation caused by temperature fluctuations from leading to wafer positioning misalignment and decreased process precision.

[0003] Currently, industry research on wafer stage materials largely focuses on fused silica and SiC ceramics. Among these materials, cordierite ceramics, due to their intrinsically low thermal expansion and excellent thermal shock resistance and chemical stability, are considered ideal candidates for wafer stages. However, in practical applications, traditional pure-phase and modified cordierite ceramics still have significant shortcomings. First, traditional simply doped cordierite ceramics are prone to large fluctuations in their coefficient of thermal expansion due to issues such as uneven crystal phase and impurity phase precipitation, making it impossible to guarantee the consistency of wafer positioning in the wafer stage. In contrast, the coefficient of thermal expansion of pure-phase cordierite ceramics is approximately 2.0 × 10⁻⁶ from room temperature to 150°C. -6 / ℃, far exceeding the ≤0.8×10 required for a wafer stage. -6 The requirement for ultra-low thermal expansion is 0.8 × 10⁻⁶ °C. While in existing technologies, the coefficient of thermal expansion is 0.8 × 10⁻⁶. -6 Cordierite ceramics with a density of / ℃ (such as Chinese patent document with publication number CN112876228A) have been publicly reported. However, the density of cordierite ceramics is less than 95%. The pore phase inside cordierite ceramics not only reduces the mechanical strength of the material, but also causes defects such as micropores and pits on the surface of cordierite ceramics after precision polishing. This makes it impossible to meet the ultra-high flatness requirement of Ra≤0.05μm for the wafer stage, which can easily lead to poor contact between the wafer and the wafer stage.

[0004] Secondly, pure phase cordierite ceramics are brittle and have low flexural strength (<150MPa). During the precision machining, assembly, and long-term use of wafer stages, they are prone to microcracks and edge chipping, which affect the stability of the equipment.

[0005] Furthermore, the sintering temperature of traditional cordierite ceramics is as high as 1350℃ or more. High temperatures can easily cause cordierite to decompose, generating high-expansion impurity phases such as mullite and corundum, which further deteriorates the thermal expansion properties of cordierite ceramics. Moreover, sintering treatment can easily lead to abnormal grain growth, increasing the difficulty of precision processing and production costs of cordierite ceramics.

[0006] It is evident that there is currently no mature cordierite ceramic solution applied to the field of semiconductor wafer stages. Summary of the Invention

[0007] In view of the shortcomings of the prior art, the purpose of this invention is to provide a low thermal expansion ceramic material, preparation method and application, which aims to solve the problem that traditional cordierite ceramics cannot have both low thermal expansion coefficient and high density, thus limiting the application of cordierite ceramics in the field of semiconductor wafer stage.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: The first aspect of this invention provides a low thermal expansion ceramic material, wherein the coefficient of thermal expansion of the low thermal expansion ceramic material is 0.3 to 0.8 × 10⁻⁶. -6 / ℃, density ≥99.2%.

[0009] The low thermal expansion ceramic material has a flexural strength ≥200MPa and a compressive strength ≥1000MPa.

[0010] The low thermal expansion ceramic material described herein includes cordierite powder, a dopant phase, and a sintering aid as its raw materials; the dopant phase includes a first dopant phase, which includes either β-lithium nepheline or La2Zr2O7; the sintering aid is a Y2O3-MgO-SiO2 composite sintering aid or a Y2O3-CaO-SiO2 composite sintering aid. 、 At least one of the following: Y2O3-MgO-SiO2-La2O3 composite sintering aid and Y2O3-MgO-SiO2-CeO2 composite sintering aid.

[0011] In the low thermal expansion ceramic material, the Y2O3-MgO-SiO2 composite sintering aid includes Y2O3, MgO, and SiO2; the mass ratio of Y2O3, MgO, and SiO2 is (1-3):(0.5-2):(1.5-3).

[0012] In the low thermal expansion ceramic material, the doped phase further includes a second doped phase; the second doped phase is ZrSiO4 or a mixture of ZrSiO4 and SiC; the mass ratio of the first doped phase to the second doped phase is 1:(1-3).

[0013] In the low thermal expansion ceramic material, the particle size D50 of the β-lithium nepheline is 0.8-1.2 μm, and the particle size D50 of the ZrSiO4 is 0.6-0.9 μm.

[0014] In the low thermal expansion ceramic material, the purity of the cordierite powder is ≥99.99%; the mass ratio of cordierite powder, dopant phase, and sintering aid is (80-88):(7-12):(3-8).

[0015] A second aspect of this invention provides a method for preparing a low thermal expansion ceramic material, comprising the following steps: S1. The raw materials used to prepare the low thermal expansion ceramic material are ball-milled and mixed to obtain a composite slurry; the composite slurry is dried and sieved to obtain a composite powder. S2. The composite powder is loaded into a mold to form a ceramic green body; S3. Sinter the ceramic green body; after sintering, cool it to room temperature to obtain a low thermal expansion ceramic material.

[0016] The method for preparing the low thermal expansion ceramic material, wherein the temperature regime for sintering in step S3 is as follows: the temperature is increased to 600°C at a heating rate of 0.5-1°C / min, and then held for 2 hours. After the holding period, the temperature is increased to 1200-1280°C at a heating rate of 3-10°C / min, and then held for 5-6 hours.

[0017] In the preparation method of the low thermal expansion ceramic material, the cooling rate in step S3 is 1-3℃ / min.

[0018] A third aspect of the present invention provides an application of a low thermal expansion ceramic material, wherein the low thermal expansion ceramic material described above is used to prepare a wafer stage.

[0019] Beneficial effects: (1) The first aspect of the present invention provides a low thermal expansion ceramic material, which has both a low coefficient of thermal expansion and high density, and its performance is superior to that of traditional cordierite ceramics. It can meet the stringent requirements of semiconductor wafer manufacturing equipment and can be used as a manufacturing material for wafer stage. The coefficient of thermal expansion of the low thermal expansion ceramic material is 0.3 to 0.8 × 10⁻⁶. -6 / ℃, meeting the ultra-low expansion requirements of the wafer stage, and the density of the low thermal expansion ceramic material is ≥99.2%, with no through-pores inside the material. This ensures that the surface of the low thermal expansion ceramic material is free of defects such as micropores and pits after precision polishing, which can meet the load-bearing requirements of ultra-high flatness of wafers. In addition, the low thermal expansion material has high mechanical strength, with a bending strength ≥200MPa and a compressive strength ≥1000MPa. This ensures that the material will not have microcracks or edge chipping that affect the stability of equipment operation during the processing, assembly and long-term use of the low thermal expansion ceramic material.

[0020] (2) The second aspect of the present invention provides a method for preparing a low thermal expansion ceramic material. By using a two-step sintering process to sinter the low thermal expansion ceramic material, the sintered low thermal expansion ceramic material is free of thermal stress cracks, and the internal microstructure of the ceramic is uniform and dense, with stable crystal phase and controllable grain size. This not only stabilizes the thermal expansion performance of the low thermal expansion ceramic material, but also provides a good foundation for the subsequent precision processing and polishing of the material, thereby ensuring the smoothness of the surface of the low thermal expansion ceramic material. Furthermore, the fine grain structure further improves the mechanical properties and thermal shock resistance of the low thermal expansion ceramic material.

[0021] (3) The third aspect of the present invention provides the application of low thermal expansion ceramic material in wafer stage. Through precision processing and polishing, the low thermal expansion ceramic material is prepared into a wafer stage with no surface defects such as scratches, pits, or micropores. The surface roughness Ra of the wafer stage is ≤0.04μm, the flatness is ≤0.02mm / m, and it has an ultra-low coefficient of thermal expansion, high density and chemical inertness, which can meet the bearing requirements of ultra-high flatness of wafers. Attached Figure Description

[0022] Figure 1 This is a flowchart of the preparation method of the low thermal expansion ceramic material provided by the present invention. Detailed Implementation

[0023] This invention provides a low thermal expansion ceramic material, its preparation method, and its application. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0024] The first aspect of this invention provides a low thermal expansion ceramic material, wherein the coefficient of thermal expansion of the low thermal expansion ceramic material is 0.3 to 0.8 × 10⁻⁶. -6 / ℃, density ≥99.2%.

[0025] The low thermal expansion ceramic material possesses both a low coefficient of thermal expansion and high density. Specifically, within a temperature range of 20–150°C, the coefficient of thermal expansion of the low thermal expansion ceramic material is 0.3–0.8 × 10⁻⁶. -6 The low thermal expansion ceramic material has a density of ≥99.2% and no through-pores inside, which not only gives it high mechanical strength, but also prevents defects such as micropores and pits from forming on its surface after precision polishing. This allows it to meet the requirements of ultra-high flatness for wafer support. Therefore, the performance of the low thermal expansion ceramic material provided by this invention is superior to that of traditional cordierite ceramics, and it can meet the stringent requirements of semiconductor wafer manufacturing equipment and can be used as a material for manufacturing wafer stages.

[0026] In a preferred embodiment, the low thermal expansion ceramic material has a flexural strength ≥200MPa and a compressive strength ≥1000MPa. The flexural strength and impact resistance of the low thermal expansion ceramic material are significantly improved, enabling it to withstand the mechanical stress of precision machining. During processing, assembly, and long-term use, the low thermal expansion ceramic material exhibits no microcracks or edge chipping. Not only is processing loss reduced, but the low thermal expansion ceramic material also has a high yield and dimensional accuracy. Furthermore, the low thermal expansion ceramic material offsets assembly stress through its own structural strength, ensuring that there is no residual stress inside the wafer stage after assembly. Even if temperature fluctuations occur during subsequent equipment operation, the wafer stage will not crack, thereby ensuring the operational stability of the equipment.

[0027] To obtain the aforementioned low thermal expansion ceramic material, in a preferred embodiment, the low thermal expansion ceramic material is cordierite ceramic, the raw materials for which include cordierite powder, a dopant phase, and a sintering aid; the dopant phase includes a first dopant phase, which is β-nepheline. This technical solution uses cordierite powder as a matrix and introduces a β-nepheline negative expansion phase as a dopant phase into the matrix, while adding a sintering aid, resulting in cordierite ceramic with an ultra-low coefficient of thermal expansion. Furthermore, it achieves a synergistic improvement in the density and chemical stability of the cordierite ceramic, thereby enabling the cordierite ceramic to be used in the fabrication of wafer carriers.

[0028] Existing sintering aids typically contain elements such as alkali metals, boron, and chlorine that react with process gases. This can lead to the wafer stage undergoing chemical reactions or leaching in process gas environments (such as HF, H2SO4, and other commonly used etching solutions in semiconductor processes, as well as SiH4, NF3, and other process gas environments), contaminating the wafer surface. Therefore, in the aforementioned raw materials for preparing cordierite ceramics, the sintering aids selected are Y2O3-MgO-SiO2 composite sintering aids and Y2O3-CaO-SiO2 composite sintering aids. 、At least one of the following composite sintering aids—Y₂O₃-MgO-SiO₂-La₂O₃ and Y₂O₃-MgO-SiO₂-CeO₂—is used. Because these composite sintering aids do not introduce elements such as alkali metals, boron, or chlorine that react with process gases, the glassy phase formed by cordierite ceramic sintering exhibits strong chemical inertness. Even in environments commonly used in semiconductor processes such as HF and H₂SO₄, or in process gases such as SiH₄ and NF₃, cordierite ceramics do not dissolve or react, thus preventing wafer surface contamination and meeting semiconductor process compatibility requirements. Furthermore, since Y₂O₃ is introduced into all of these composite sintering aids, Y₂O₃ and other components in the composite sintering aid can form a low-melting-point glassy phase and fill the gaps in the cordierite powder, thereby enabling low-temperature densification sintering of cordierite ceramics.

[0029] To achieve low thermal expansion and high density in cordierite ceramics, and to improve their mechanical properties, in a preferred embodiment, the Y₂O₃-MgO-SiO₂ composite sintering aid comprises Y₂O₃, MgO, and SiO₂; the mass ratio of Y₂O₃, MgO, and SiO₂ is (1–3):(0.5–2):(1.5–3). This mass ratio of composite sintering aid allows it to form a highly efficient synergistic effect with the cordierite matrix and doped phases such as β-lithium nepheline within a low-temperature sintering range of 1220–1280℃. Specifically, Y₂O₃, as a component for grain regulation and grain boundary strengthening, when added at the above mass ratio, can segregate at the cordierite grain interface during the sintering process of cordierite ceramics, effectively hindering grain migration and merging, controlling the micro-grain size within the fine grain range of 2–5 μm, achieving fine grain strengthening while suppressing the precipitation of high-expansion impurity phases, and reducing the difficulty of precision machining of the material. Secondly, when MgO is added at the above mass ratio, it can synergistically form a low-melting-point glassy phase with Y₂O₃ and SiO₂ and uniformly fill the gaps between cordierite powder particles. Compared with solid-state sintering, this provides a basis for the densification of cordierite ceramics, ensuring that the low-thermal-expansion ceramic material simultaneously possesses a low coefficient of thermal expansion and high density. Furthermore, when SiO2 is added in the above mass ratio, it can regulate the melting point and fluidity of the glass phase, and avoid excessive formation of the glass phase, which would increase the brittleness of cordierite ceramics. Therefore, when Y2O3, MgO and SiO2 are compounded in the above mass ratio, cordierite ceramics can achieve low-temperature densification and improve their mechanical properties.

[0030] In semiconductor processes such as wafer lithography and coating, temperature fluctuations can cause thermal stress within cordierite ceramic materials. If the thermal shock resistance of cordierite ceramics is insufficient, thermal stress can induce microcracks within the material, damaging the flatness and structural integrity of the wafer stage. Therefore, to further improve the thermal shock resistance of cordierite ceramics, in a preferred embodiment, a Y2O3-MgO-SiO2-La2O3 composite sintering aid can be used. This aid can optimize the toughness of the grain boundary glass phase, increasing the thermal shock resistance temperature difference of cordierite ceramics to over 300°C, thus adapting to scenarios with large temperature fluctuations in etching processes.

[0031] When cordierite ceramics are sintered in a vacuum process, the reactivity of MgO is weaker than that in an aerobic sintering process. This is detrimental to the synergistic formation of a low-melting-point glassy phase by MgO, Y₂O₃, and SiO₂, thus compromising the density of the cordierite ceramics. In a preferred embodiment, a Y₂O₃-CaO-SiO₂ composite sintering aid can be used. Under vacuum sintering conditions, CaO has higher reactivity than MgO. Therefore, by replacing MgO with CaO in the Y₂O₃-MgO-SiO₂ composite sintering aid, the density of cordierite ceramics sintered using the vacuum sintering process can be guaranteed.

[0032] To achieve higher density in cordierite ceramics, existing cordierite ceramics typically require long sintering holding times, resulting in high sintering energy consumption. Therefore, to reduce sintering energy consumption, in a preferred embodiment, a Y₂O₃-MgO-SiO₂-CeO₂ composite sintering aid can be used. During sintering, the Y₂O₃-MgO-SiO₂-CeO₂ composite sintering aid forms a Y-Mg-Si-Ce quaternary multi-element glass phase with a lower eutectic point. This allows for earlier formation of the liquid phase during sintering, further optimizing the flowability of the grain boundary glass phase, improving the densification efficiency of the material, and shortening the sintering holding time to 4–5 hours without affecting the performance of the cordierite ceramic.

[0033] Secondly, among the raw materials for preparing cordierite ceramics mentioned above, β-lithium nepheline (LiAlSiO4) has a coefficient of thermal expansion of ≈-4.0×10⁻⁶ at 20–150 °C. -6 While the negative expansion effect of the doped phase at a temperature of 0.5°C can precisely offset the positive expansion of the cordierite phase, thus achieving ultra-low thermal expansion of cordierite ceramics, it cannot stabilize the overall thermal expansion performance of the cordierite ceramics. Therefore, in a preferred embodiment, to stabilize the overall thermal expansion performance of cordierite ceramics, the doped phase further includes a second doped phase, which is a low-expansion ZrSiO4 phase (thermal expansion coefficient ≈ 0.5 × 10⁻⁶). -6Specifically, ZrSiO4 decomposes at high temperatures to produce zirconium oxide, which refines cordierite grains and fills grain boundaries, suppressing thermal expansion fluctuations caused by crystal phase distortion and improving the mechanical strength of cordierite ceramics. Secondly, both ZrSiO4 and β-nepheline are 99.99% high-purity powders with impurity content ≤0.05%, avoiding the precipitation of high-expansion impurity phases during sintering. Therefore, the coefficient of thermal expansion of cordierite ceramics can be stably controlled within the range of 0.3–0.8 × 10⁻⁶ °C in the 20–50 °C range. -6 / ℃, which can fully meet the ultra-low expansion requirements of the wafer stage; and the batch-to-batch thermal expansion coefficient of cordierite ceramic fluctuates by ≤3%, with good thermal shock resistance. When the equipment generates heat or the ambient temperature fluctuates, the wafer stage does not have obvious thermal deformation or cracking problems, and can ensure wafer positioning accuracy ≤±0.001mm.

[0034] In a composite doped phase composed of β-nepheline (first doped phase) and ZrSiO4 (second doped phase), if the proportion of β-nepheline is too high, its strong negative expansion effect will cause the positive expansion of cordierite to be completely offset, resulting in a low coefficient of thermal expansion of cordierite ceramics or even overall negative expansion. When the ambient temperature rises, the shrinkage of the material can easily cause poor bonding between the wafer stage and the wafer, and positioning misalignment. On the other hand, if the proportion of ZrSiO4 is too high, its own low expansion positive expansion characteristics will weaken the negative expansion offsetting effect of β-nepheline on cordierite. Based on this, the present invention found that when the mass ratio of β-nepheline to ZrSiO4 is controlled at 1: (1~3), the thermal expansion performance of cordierite ceramics can be well stabilized.

[0035] In a composite doped phase composed of β-nepheline and ZrSiO4, if the β-nepheline particle size is too fine, its specific surface area is large, resulting in excessively high sintering activity. This leads to the rapid generation of a large amount of liquid phase during sintering, causing local enrichment and encapsulation of the liquid phase within the cordierite grains. This hinders the normal bonding and densification between cordierite crystal phases. Furthermore, excessive glass phase formed during liquid phase cooling can cause fluctuations in the thermal expansion coefficient of cordierite ceramics. Conversely, if the β-nepheline particle size is too coarse, its specific surface area is small, resulting in low sintering activity. The amount of liquid phase generated is insufficient to fill the gaps between cordierite crystals, thus affecting the density of the cordierite ceramic. Based on this, as a further optimization, the present invention found that when β-nepheline with a particle size D50 of 0.8 to 1.2 μm is used as the first doping phase, β-nepheline can not only help fill the gaps between cordierite crystals and further improve the density of cordierite ceramics, but also stabilize the thermal expansion coefficient of cordierite ceramics.

[0036] In the composite doped phase composed of β-nepheline and ZrSiO4, when the ZrSiO4 particle size is relatively coarse, the decomposition temperature of ZrSiO4 is higher, which cannot match the low-temperature sintering temperature range of cordierite ceramics. This results in a low content of zirconium oxide produced by the decomposition of ZrSiO4, thus losing its function of fine grain strengthening and thermal expansion stabilization. Conversely, when the ZrSiO4 particle size is relatively fine, the ZrSiO4 decomposes too quickly, leading to a large amount of zirconium oxide being generated in the early stage of cordierite grain formation, thereby hindering the formation of cordierite crystals. The interphase bonding hinders the densification of cordierite ceramics during sintering. Based on this, as a further optimization, this invention found that using ZrSiO4 with a particle size D50 of 0.6-0.9 μm as the second doping phase can match the low-temperature sintering range of cordierite ceramics. Furthermore, the zirconium oxide content generated by the decomposition of ZrSiO4 during sintering is moderate, and the zirconium oxide can be uniformly dispersed at the cordierite grain boundaries, acting as an obstacle to cordierite grain growth, thereby achieving fine-grain strengthening.

[0037] In a preferred embodiment, La₂Zr₂O₇ can be used instead of β-nepheline to control the thermal expansion coefficient of the cordierite ceramic within the range of 0.3–0.6 × 10⁻⁶. -6 / ℃, which can adapt to high-temperature coating processes. The second doped phase can also be a mixture of ZrSiO4 and SiC, so that the high hardness of SiC can be used to improve the wear resistance of the wafer stage surface of cordierite ceramic.

[0038] The purity of cordierite powder directly affects the purity of the ceramic crystal phase, thermal expansion stability, and mechanical properties. Therefore, in the aforementioned raw materials for preparing cordierite ceramics, the cordierite powder is synthesized via a sol-gel method or hydrothermal method, and then dried and calcined. Using these methods yields cordierite powder with a uniform crystal phase, no agglomeration, a purity ≥99.99%, and no impurity phase introduction. This avoids the problems of cordierite crystal phase distortion and thermal expansion coefficient fluctuations caused by impurities, ensuring the intrinsic low thermal expansion characteristics of the cordierite matrix. This provides a pure crystal phase basis for the precise cancellation of thermal expansion between cordierite and β-nepheline. Secondly, the cordierite powder obtained by the above method is a submicron-sized powder with a large specific surface area and abundant surface active sites. Its sintering activity is much higher than that of powder obtained by solid-phase method, enabling the cordierite powder to react rapidly with sintering aids in the low-temperature sintering range. Furthermore, the liquid phase filling effect achieves efficient densification, thus achieving a density of ≥99.2% for cordierite ceramics without excessively high sintering temperatures. It also effectively suppresses the high-temperature decomposition of cordierite, preventing the formation of highly expanding impurity phases such as mullite and corundum, ensuring crystal phase stability. Moreover, the cordierite powder obtained by the above method has a uniform crystal phase and no component segregation. After drying and low-temperature calcination, there is no hard agglomeration, allowing the cordierite powder to achieve uniform particle-level mixing with β-lithium nepheline, ZrSiO4, and sintering aids. This avoids problems such as localized thermal expansion imbalance, insufficient densification, and uneven mechanical properties caused by uneven powder mixing.

[0039] Finally, in the aforementioned raw materials for preparing cordierite ceramics, the mass ratio of cordierite powder, dopant phase, and sintering aid is (80-88):(7-12):(3-8). This technical solution, by optimizing the mass ratio of cordierite powder, dopant phase, and sintering aid, ensures that the sintered cordierite ceramics have an ultra-low coefficient of thermal expansion and achieves a synergistic improvement in the density, mechanical properties, and chemical stability of the cordierite ceramics. Specifically, the dopant phase is dispersed in the cordierite matrix in an appropriate proportion, which can fully utilize the negative expansion compensation effect of β-nepheline and the low expansion stability and grain refinement effect of ZrSiO4, while avoiding damage to the continuous structure of the cordierite matrix due to an excessively high proportion of the dopant phase, resulting in cordierite ceramics with excellent density obtained by low-temperature sintering. Secondly, during the low-temperature sintering process, the liquid phase content formed in the raw material system is moderate, meeting the requirements for low-temperature sintering of cordierite ceramics. Furthermore, the cordierite matrix and doped phase particles are not excessively encapsulated by the liquid phase, allowing the negative expansion effect of β-lithium nepheline and the grain-refining strengthening effect of ZrSiO4 to be fully utilized. This ensures that the cordierite ceramics after low-temperature sintering will not lose their ultra-low expansion characteristics due to phase imbalance, nor will they be affected by insufficient mechanical properties in terms of precision machining and practical performance.

[0040] As an example, cordierite powder can be pre-synthesized using the following sol-gel method. First, magnesium nitrate (Mg(NO3)2·6H2O) and aluminum nitrate (Al(NO3)3·9H2O) are added to a mixed solvent of anhydrous ethanol and deionized water (volume ratio 3:1). After stirring and dissolving, 0.5–1 wt% nitric acid is added as a catalyst, and the mixture is stirred in a 60°C water bath for 1–2 hours until a uniform, transparent solution is obtained. Then, tetraethyl orthosilicate is added dropwise at a rate of 1–2 drops / second as a silicon source, and stirring continues for 3–4 hours to form a transparent sol. Next, the sol is allowed to stand at room temperature for 12–24 hours to age, forming a wet gel. After pre-synthesis, the wet gel is dried in an 80°C oven for 4–6 hours, followed by calcination at 600°C in air for 2 hours. After calcination, the sintered material is ground and sieved through a 200-mesh sieve to obtain highly active cordierite powder.

[0041] like Figure 1 As shown, a second aspect of the present invention provides a method for preparing a low thermal expansion ceramic material, used to prepare the cordierite ceramic material with a low coefficient of thermal expansion as described above, comprising the following steps: S1. Using anhydrous ethanol as the dispersion medium and zirconium oxide as the grinding medium (ball-to-material ratio 6:1), the raw materials for preparing the low thermal expansion ceramic material are ball-milled and mixed to obtain a composite slurry; the composite slurry is dried and sieved to obtain a composite powder. S2. The composite powder is loaded into a mold to form a ceramic green body; S3. The ceramic green body is placed in a box-type sintering furnace and sintered in a two-step low temperature atmosphere. After sintering, the sintering furnace is cooled to obtain a low thermal expansion ceramic material.

[0042] First, in the aforementioned method for preparing low thermal expansion ceramic materials, the ball milling time for the raw materials is 4–6 hours, and the ball mill speed is 300–350 r / min, which enables the ball milling to obtain a uniform mixed slurry. After obtaining the composite slurry, the composite slurry is placed in an 80℃ oven for drying. After drying, the material is sieved (100 mesh) to obtain composite powder.

[0043] Secondly, in the aforementioned method for preparing low thermal expansion ceramic materials, after the composite powder is loaded into the mold, it can be pre-formed by dry pressing (pressure 150–200 MPa, holding pressure 2–3 min), and then formed by cold isostatic pressing (forming pressure 250–300 MPa, holding pressure time 8–10 min) to obtain a cordierite ceramic green body. The cordierite ceramic green body obtained by the above forming method has a density ≥65%, which can ensure the consistency of forming and match the customized size requirements of the wafer stage.

[0044] Then, in the aforementioned method for preparing low thermal expansion ceramic materials, the first step involves heating the sintering furnace to 600℃ at a heating rate of 0.5–1℃ / min, and then holding it at that temperature for 2 hours. After holding, the second step involves heating the furnace to 1200–1280℃ at a heating rate of 3–10℃ / min, and then holding it at that temperature for 5–6 hours. By performing a two-step low-temperature sintering process on cordierite ceramics, the problems of excessive internal and external temperature differences and thermal stress concentration caused by rapid heating in cordierite ceramic green bodies can be avoided, preventing structural defects such as cracking and deformation during the sintering process. Secondly, the two-step low-temperature sintering process allows the cordierite ceramic green body to complete the debinding and densification processes in stages. Specifically, the first sintering step ensures that the binder and dispersant in the cordierite ceramic green body are fully debinded, avoiding the formation of pores and microcracks inside the cordierite ceramic. The second sintering step allows the low-melting-point glass phase to efficiently fill the gaps in the powder, resulting in cordierite ceramic with high density. Furthermore, the second sintering temperature is lower than the traditional cordierite ceramic sintering temperature, which can effectively inhibit the decomposition of cordierite to form high-expansion impurity phases such as mullite and corundum, giving cordierite ceramic an ultra-low coefficient of thermal expansion. At the same time, low-temperature sintering can inhibit the rapid growth of cordierite grains, thereby controlling the size of cordierite grains and improving the precision machinability of the material.

[0045] Furthermore, during the low-temperature sintering process, the slow heating allows for uniform heat conduction within the cordierite ceramic green body. This promotes simultaneous phase formation and densification processes in different regions of the green body, preventing microscopic defects caused by uneven local sintering. Therefore, the two-step low-temperature sintering process results in cordierite ceramics free from thermal stress cracks, with a uniform and dense internal microstructure, stable crystal phases, and controllable grain size. This not only stabilizes the thermal expansion properties of cordierite ceramics but also provides a good foundation for subsequent precision processing and polishing, ensuring the smoothness of the cordierite ceramic surface. Moreover, the fine-grained structure further enhances the mechanical properties and thermal shock resistance of cordierite ceramics.

[0046] After sintering, the sintering furnace is cooled to room temperature at a rate of 1-3℃ / min. This avoids internal stress, microcracks and structural deformation in the glass phase inside the cordierite ceramic due to excessively rapid cooling, which helps to ensure the structural integrity, dimensional accuracy and stability of various properties of the cordierite ceramic.

[0047] The third aspect of this invention provides the application of low thermal expansion ceramic materials in wafer stages. Through precision machining and polishing, the low thermal expansion ceramic materials are prepared into wafer stages with no surface defects such as scratches, pits, or micropores. The surface roughness Ra of the wafer stage is ≤0.04μm, the flatness is ≤0.02mm / m, and it has an ultra-low coefficient of thermal expansion, high density, and chemical inertness, which can meet the requirements of ultra-high flatness of wafers.

[0048] The following examples and comparative examples further illustrate the technical solution of the present invention.

[0049] Example 1 This embodiment provides a low thermal expansion ceramic material. The raw materials for preparing the low thermal expansion ceramic material include cordierite powder, a dopant phase, a sintering aid, a binder PVA, and a dispersant (ammonium citrate). The mass ratio of cordierite powder, dopant phase, sintering aid, binder PVA, and dispersant is 85:9:5:2:1.

[0050] The doped phase includes a first doped phase and a second doped phase. The first doped phase is β-nepheline with a particle size D50 of 1.0 μm, and the second doped phase is ZrSiO4 with a particle size D50 of 0.7 μm. The mass ratio of the first doped phase to the second doped phase is 1:2.

[0051] The sintering aid is a Y2O3-MgO-SiO2 composite sintering aid. The Y2O3-MgO-SiO2 composite sintering aid comprises Y2O3, MgO, and SiO2. The mass ratio of Y2O3, MgO, and SiO2 is 3:0.5:1.5.

[0052] This embodiment also provides a method for preparing a low thermal expansion ceramic material, including the following steps: S1. Using anhydrous ethanol as the dispersion medium and zirconium oxide as the grinding medium (ball-to-material ratio 6:1), the raw materials for preparing the low thermal expansion ceramic material are ball-milled and mixed to obtain a composite slurry; the composite slurry is dried and sieved to obtain a composite powder. S2. The composite powder is loaded into a mold to form a ceramic green body; S3. The ceramic green body is placed in a box-type sintering furnace and sintered in a two-step low temperature atmosphere. After sintering, the sintering furnace is cooled to obtain a low thermal expansion ceramic material.

[0053] Specifically, in step S1, the ball milling time for the raw materials is 4 hours, and the ball mill speed is 300 r / min.

[0054] In step S2, after the composite powder is loaded into the mold, the composite powder is first dry-pressed for pre-forming (pressure of 150MPa, holding pressure for 2min), and then cold isostatic pressing is used for forming (forming pressure of 250MPa, holding pressure for 8min) to obtain cordierite ceramic green body.

[0055] In step S3, the temperature is increased to 600℃ at a heating rate of 0.5℃ / min, and then held for 2 hours. After the holding period, the temperature is increased to 1200℃ at a heating rate of 3℃ / min, and then held for 5 hours. After sintering, the sintering furnace is cooled to room temperature at a cooling rate of 1℃ / min.

[0056] Example 2 This embodiment provides a low thermal expansion ceramic material. The raw materials for preparing the low thermal expansion ceramic material include cordierite powder, a dopant phase, a sintering aid, a binder PVA, and a dispersant (ammonium citrate). The mass ratio of cordierite powder, dopant phase, sintering aid, binder PVA, and dispersant is 80:7:3:1:0.5.

[0057] The doped phase includes a first doped phase and a second doped phase. The first doped phase is β-nepheline with a particle size D50 of 0.8 μm, and the second doped phase is ZrSiO4 with a particle size D50 of 0.6 μm. The mass ratio of the first doped phase to the second doped phase is 1:1.

[0058] The sintering aid is a Y2O3-MgO-SiO2 composite sintering aid. The Y2O3-MgO-SiO2 composite sintering aid comprises Y2O3, MgO, and SiO2. The mass ratio of Y2O3, MgO, and SiO2 is 1:0.5:1.5.

[0059] This embodiment also provides a method for preparing a low thermal expansion ceramic material, including the following steps: S1. Using anhydrous ethanol as the dispersion medium and zirconium oxide as the grinding medium (ball-to-material ratio 6:1), the raw materials for preparing the low thermal expansion ceramic material are ball-milled and mixed to obtain a composite slurry; the composite slurry is dried and sieved to obtain a composite powder. S2. The composite powder is loaded into a mold to form a ceramic green body; S3. The ceramic green body is placed in a box-type sintering furnace and sintered in a two-step low temperature atmosphere. After sintering, the sintering furnace is cooled to obtain a low thermal expansion ceramic material.

[0060] Specifically, in step S1, the ball milling time for the raw materials is 6 hours, and the ball mill speed is 350 r / min.

[0061] In step S2, after the composite powder is loaded into the mold, the composite powder is first dry-pressed for pre-forming (pressure of 200MPa, holding pressure for 3min), and then cold isostatic pressing is used for forming (forming pressure of 300MPa, holding pressure for 10min) to obtain cordierite ceramic green body.

[0062] In step S3, the temperature is increased to 600℃ at a heating rate of 1℃ / min, and then held for 2 hours. After the holding period, the temperature is increased to 1280℃ at a heating rate of 3℃ / min, and then held for 6 hours. After sintering, the sintering furnace is cooled to room temperature at a cooling rate of 3℃ / min.

[0063] Example 3 This embodiment provides a low thermal expansion ceramic material. The raw materials for preparing the low thermal expansion ceramic material include cordierite powder, a dopant phase, a sintering aid, a binder PVA, and a dispersant (ammonium citrate). The mass ratio of cordierite powder, dopant phase, sintering aid, binder PVA, and dispersant is 88:12:8:4:1.5.

[0064] The doped phase includes a first doped phase and a second doped phase. The first doped phase is β-nepheline with a particle size D50 of 1.2 μm, and the second doped phase is ZrSiO4 with a particle size D50 of 0.9 μm. The mass ratio of the first doped phase to the second doped phase is 1:3.

[0065] The sintering aid is a Y2O3-MgO-SiO2 composite sintering aid. The Y2O3-MgO-SiO2 composite sintering aid comprises Y2O3, MgO, and SiO2. The mass ratio of Y2O3, MgO, and SiO2 is 3:2:3.

[0066] This embodiment also provides a method for preparing a low thermal expansion ceramic material, which is the same as the preparation method provided in Example 1.

[0067] Comparative Example 1 This comparative example provides a low thermal expansion ceramic material, which differs from Example 1 only in that the mass ratio of cordierite powder, dopant phase, sintering aid, binder PVA, and dispersant (ammonium citrate) is 85:5:5:2:1.

[0068] This comparative example also provides a method for preparing a low thermal expansion ceramic material, which is the same as the method provided in Example 1.

[0069] Comparative Example 2 This comparative example provides a low thermal expansion ceramic material, differing from Example 1 only in that the sintering aid is a MgO-SiO2 composite sintering aid, with a MgO to SiO2 mass ratio of 1:3.

[0070] This comparative example also provides a method for preparing a low thermal expansion ceramic material, which is the same as the method provided in Example 1.

[0071] Comparative Example 3 This comparative example provides a low thermal expansion ceramic material, which differs from Example 1 only in that the sintering aid is a Y2O3-MgO-SiO2 composite sintering aid, and the mass ratio of Y2O3, MgO and SiO2 is 0.5:0.5:4.

[0072] This comparative example also provides a method for preparing a low thermal expansion ceramic material, which is the same as the method provided in Example 1.

[0073] Comparative Example 4 This comparative example provides a low thermal expansion ceramic material, which differs from Example 1 only in that the mass ratio of the first doped phase (β-nepheline) to the second doped phase (ZrSiO4) is 2:1. This comparative example also provides a method for preparing the low thermal expansion ceramic material, which is the same as the method provided in Example 1.

[0074] Comparative Example 5 This comparative example provides a low thermal expansion ceramic material, differing from Example 1 only in that the mass ratio of the first doped phase (β-nepheline) and the second doped phase (ZrSiO4) is 1:3.5. This comparative example also provides a method for preparing the low thermal expansion ceramic material, which is the same as the method provided in Example 1.

[0075] Comparative Example 6 This comparative example provides a low thermal expansion ceramic material, which differs from Example 1 only in that... The first doped phase (β-nepheline) has a D50 particle size of 1.0 μm, and the second doped phase (ZrSiO4) has a D50 particle size of 1.5 μm (ZrSiO4 is coarser).

[0076] This comparative example also provides a method for preparing a low thermal expansion ceramic material, which is the same as the method provided in Example 1.

[0077] Comparative Example 7 This comparative example provides a low thermal expansion ceramic material, the raw materials for which are the same as those provided in Example 1.

[0078] This comparative example also provides a method for preparing a low thermal expansion ceramic material, including the following steps: S1. Using anhydrous ethanol as the dispersion medium and zirconium oxide as the grinding medium (ball-to-material ratio 6:1), the raw materials for preparing the low thermal expansion ceramic material are ball-milled and mixed to obtain a composite slurry; the composite slurry is dried and sieved to obtain a composite powder. S2. The composite powder is loaded into a mold to form a ceramic green body; S3. The ceramic green body is placed in a box-type sintering furnace and sintered at high temperature in an air atmosphere. After sintering, the sintering furnace is cooled to obtain a low thermal expansion ceramic material.

[0079] Specifically, in step S1, the ball milling time for the raw materials is 4 hours, and the ball mill speed is 300 r / min.

[0080] In step S2, after the composite powder is loaded into the mold, the composite powder is first dry-pressed for pre-forming (pressure of 150MPa, holding pressure for 2min), and then cold isostatic pressing is used for forming (forming pressure of 250MPa, holding pressure for 8min) to obtain cordierite ceramic green body.

[0081] In step S3, the high-temperature sintering process is as follows: the temperature is increased to 600℃ at a heating rate of 5℃ / min, and then held for 2 hours. After the holding period, the temperature is increased to 1200℃ at a heating rate of 15℃ / min, and then held for 6 hours. The temperature is then lowered and cooled with the furnace.

[0082] The low thermal expansion ceramic materials prepared in the above embodiments and comparative examples were tested for their coefficient of thermal expansion (tested according to the provisions of standard GB / T 16535-2008), density (tested according to the provisions of standard GB / T 25995-2010), flexural strength and compressive strength (tested according to the provisions of standard GB / T 4740-2024).

[0083]

[0084] As shown in the table above, the coefficient of thermal expansion of the low thermal expansion ceramic materials provided in Examples 1-3 is <0.8×10⁻⁶. -6 The low thermal expansion ceramic material has a density of ≥99.4%, a flexural strength of ≥200MPa, and a compressive strength of ≥1000MPa, which are superior to traditional cordierite ceramics. Therefore, the low thermal expansion ceramic material provided by this invention can meet the stringent requirements of semiconductor wafer manufacturing equipment and can be used as a manufacturing material for wafer stage.

[0085] Furthermore, comparing Comparative Example 1 with Example 1, it was found that the coefficient of thermal expansion of the low thermal expansion ceramic material provided by Comparative Example 1 increased. This is because, compared with Example 1, the amount of doped phase (β-lithium nepheline, ZrSiO4) in Comparative Example 1 was reduced, and the negative expansion compensation and thermal expansion stabilization effect of the doped phase was weakened, which could not effectively offset the positive expansion of the cordierite matrix, resulting in an increase in the overall coefficient of thermal expansion of the material.

[0086] Furthermore, comparing Comparative Example 2 with Example 1, it was found that the coefficient of thermal expansion of the low-thermal-expansion ceramic material provided in Comparative Example 2 increased. This is because Comparative Example 2 used a MgO-SiO2 binary sintering aid. During the sintering process, due to the lack of grain control effect of Y2O3, the cordierite grains grew abnormally during sintering, failing to achieve fine-grain strengthening, and easily precipitating high-expansion impurity phases such as mullite, thus increasing the coefficient of thermal expansion of the material. In addition, the melting point of the MgO-SiO2 binary glass phase is relatively high, resulting in insufficient fluidity at low-temperature sintering, which easily leads to insufficient filling of powder gaps, resulting in decreased density and mechanical properties.

[0087] Furthermore, comparing Comparative Example 3 with Example 1, it was found that the coefficient of thermal expansion of the low thermal expansion ceramic material provided in Comparative Example 3 increased. This is because the proportion of Y2O3 in the ternary composite sintering aid used in Comparative Example 3 was too low and the proportion of SiO2 was too high, resulting in a weakened grain control effect of Y2O3 agglomeration grain boundaries, larger grain size, a small amount of high-expansion impurity phase precipitation, and insufficient fine grain strengthening effect, which leads to a decrease in the mechanical strength of the low thermal expansion ceramic material. Moreover, the high proportion of SiO2 resulted in poor fluidity of the glass phase during sintering, leading to a decrease in the density of the material.

[0088] Furthermore, comparing Comparative Example 4 with Example 1, it was found that the low thermal expansion ceramic material provided by Comparative Example 4 exhibited overall negative thermal expansion. This was because the amount of the first doped phase (β-nepheline) was significantly increased, and the negative expansion effect excessively compensated for the positive expansion of cordierite.

[0089] Furthermore, comparing Comparative Example 5 with Example 1, it was found that the coefficient of thermal expansion of the low thermal expansion ceramic material provided in Comparative Example 5 increased. This was because the amount of the second doped phase (ZrSiO4) was significantly increased, weakening the negative expansion compensation effect of β-nepheline. Excessive ZrSiO4 content would disrupt the continuous structure of the cordierite matrix, affecting the material's density and mechanical properties.

[0090] Furthermore, comparing Comparative Example 6 with Example 1, it was found that the coefficient of thermal expansion of the low thermal expansion ceramic material provided in Comparative Example 6 increased. This was because the coarser second doped phase (ZrSiO4) led to an increase in its decomposition temperature. Under the original sintering regime, the content of zirconium oxide produced by decomposition decreased, resulting in the loss of its effect on refining cordierite grains (affecting mechanical strength) and stabilizing thermal expansion. In addition, the coarser ZrSiO4 particles had larger volumes and could not fill the tiny gaps between cordierite grain boundaries, resulting in the formation of a small number of closed pores inside the ceramic material, causing a slight decrease in density compared to Example 1.

[0091] Furthermore, comparing Comparative Example 7 with Example 1, it was found that the rapid heating in Comparative Example 7 led to a large temperature difference between the inside and outside of the ceramic green body and a concentration of thermal stress, which in turn caused microcracks to form inside the material, resulting in a decrease in the density and mechanical properties of the material. At the same time, the thermal stress inside the material caused local crystal phase distortion, and there was no synchronous phase formation process of crystal phase with slow heating. Therefore, it led to an imbalance in the offset of thermal expansion, resulting in an increase in the coefficient of thermal expansion of the material.

[0092] It is understood that those skilled in the art can make equivalent substitutions or modifications to the technical solution and inventive concept of the present invention, and all such substitutions or modifications should fall within the protection scope of the appended claims.

Claims

1. A low thermal expansion ceramic material, characterized in that, The coefficient of thermal expansion of the low-thermal-expansion ceramic material is 0.3 to 0.8 × 10⁻⁶. -6 / ℃, density ≥99.2%.

2. The low thermal expansion ceramic material according to claim 1, characterized in that, The low thermal expansion ceramic material has a flexural strength ≥200MPa and a compressive strength ≥1000MPa.

3. The low thermal expansion ceramic material according to claim 1 or 2, characterized in that, The raw materials for preparing the low thermal expansion ceramic material include cordierite powder, a dopant phase, and a sintering aid; the dopant phase includes a first dopant phase, which is β-lithium nepheline or La2Zr2O7; the sintering aid is a Y2O3-MgO-SiO2 composite sintering aid or a Y2O3-CaO-SiO2 composite sintering aid. 、 At least one of the following: Y2O3-MgO-SiO2-La2O3 composite sintering aid and Y2O3-MgO-SiO2-CeO2 composite sintering aid.

4. The low thermal expansion ceramic material according to claim 3, characterized in that, The Y2O3-MgO-SiO2 composite sintering aid includes Y2O3, MgO, and SiO2; the mass ratio of Y2O3, MgO, and SiO2 is (1-3):(0.5-2):(1.5-3).

5. The low thermal expansion ceramic material according to claim 3, characterized in that, The doped phase further includes a second doped phase; the second doped phase is ZrSiO4 or a mixture of ZrSiO4 and SiC; the mass ratio of the first doped phase to the second doped phase is 1:(1~3).

6. The low thermal expansion ceramic material according to claim 4, characterized in that, The β-nepheline has a particle size D50 of 0.8–1.2 μm, and the ZrSiO4 has a particle size D50 of 0.6–0.9 μm.

7. The low thermal expansion ceramic material according to claim 3, characterized in that, The purity of the cordierite powder is ≥99.99%; the mass ratio of cordierite powder, dopant phase, and sintering aid is (80-88):(7-12):(3-8).

8. A method for preparing a low thermal expansion ceramic material, characterized in that, The preparation of the low thermal expansion ceramic material according to any one of claims 1-7 includes the following steps: S1. The raw materials used to prepare the low thermal expansion ceramic material are ball-milled and mixed to obtain a composite slurry; the composite slurry is dried and sieved to obtain a composite powder; S2. The composite powder is loaded into a mold to form a ceramic green body; S3. Sinter the ceramic green body; after sintering, cool it to room temperature to obtain a low thermal expansion ceramic material.

9. The method for preparing the low thermal expansion ceramic material according to claim 8, characterized in that, In step S3, the temperature regime for sintering is as follows: the temperature is increased to 600℃ at a heating rate of 0.5 to 1℃ / min, and then held for 2 hours. After the holding period, the temperature is increased to 1200 to 1280℃ at a heating rate of 3 to 10℃ / min, and then held for 5 to 6 hours. The cooling rate is 1 to 3℃ / min.

10. An application of a low thermal expansion ceramic material as described in any one of claims 1-7, characterized in that, The low thermal expansion ceramic material described above is used to prepare a wafer stage.

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